that's an overly hard and fast rule. i find that instrumental electronic music is amazing for work. it focuses rather than distracts, providing nice mental bumpers. i actually can't stand unnatural or played back sounds of the sea or nature and other such sounds, as i find it too distracting. it doesn't provide any focusing structure and allows my mind to wonder and relax.

and people complaining about headphones don't buy the right ones. i use beyerdynamic headphones and could wear them all day.